Customers referred by Twitter now average a $US90 purchase, a 25% increase year-over-year. (That’s more than the average order value of $US86 attributable to Facebook users.)

Still, the biggest spending e-commerce customers are those who were not referred by any channel. They went to the e-commerce site directly. Of course, those “no referrals” may have been influenced by a brand’s Facebook page, an ad they saw alongside Google search results, or some other form of marketing or advertising. One in three global consumers say social media has influenced their purchases, according to Ipsos OTX.

Pinterest doesn’t yet offer any paid advertising opportunities that brands and retailers might use to promote sales and offers, which probably explains Pinterest’s dramatic dip in average order value during the 2012 holiday quarter.

Although social media shows promise as an e-commerce referrer, the volume is still not there. Search and email still trump social media when it comes to conversion rates. Leading the charge is AOL Search with a 4% conversion rate.